The consumer has a large number of requirements in the field of cosmetic emulsions for skin and hair care: Apart from the cleansing and care effects, which determine the intended use, value is placed on such different parameters as the highest possible dermatological tolerability, good re-oiling properties, elegant appearance, optimum sensorial impression and storage stability.
Formulations which are employed for cleansing and care of human skin and of hair as a rule comprise, in addition to a number of surface-active substances, oil substances and water. Oil substances/emollients which are employed are, for example, hydrocarbons, ester oils and plant and animal oils/fats/waxes. To meet the high requirements of the market with respect to sensorial properties and optimum dermatological tolerability, novel oil substances and emulsifier mixtures are continuously being developed and tested.
It is furthermore known that relatively large amounts of the ultraviolet content in natural and artificial light sources (e.g., UV-A 320-390 nm; UV-B 280-320 nm; UV-C 100 or 200-280 nm) lead to damage to the human skin.
UV-A radiation mainly has the effect of ageing the skin (thinning of the epidermis and degeneration of connective tissue, pigment disorders), while UV-B and UV-C lead to sunburn and skin cancer.
Leisure activities which have changed in recent years with longer periods in open air and, in particular, extensive sunbathing to achieve the “healthy tan” have, however, against the background of medical findings and the awareness of the lack of natural protection mechanisms of the skin by pigment formation and solar acclimatization by thickening of the horny layer, shifted the need for adequate protection against intensive UV radiation far into the foreground. It has been intensified significantly by the discussion of the decrease and thinning of the Antarctic ozone hole and the associated increase in the intensity of UV-A and UV-B radiation on the earth's surface.
This becomes clear from the increasing turnovers in recent years of products with high sun protection factors (SPF). These are mainly conventional sunscreen formulations (sun milk, sun oil) with the primary intended use of sunbathing, but increasingly also the so-called care products for the face, body and hair, such as day and night creams, conditioners, lotions, (hydro, lipo)gels, (lip)sticks and sprays, pharmaceutical formulations and to a small extent products of decorative cosmetics, which are predominantly commercially available in the form of oils and liquid, cream-like or ointment/paste-like W/O and O/W emulsions.
The light protection factor (LPF) or also SPF is a coefficient which expresses the ability of a product to prevent sunburn by the sun. Light protection with a factor of 60 therefore protects against the occurrence of sunburn for twice as long as a product with factor 30 and correspondingly three times as long as a product with factor 20.
These higher light protection factors are in most cases generated by an increase in the concentration of UV light protection filter substances in the formulation.
Since 1995 light protection factors have been measured by the same international standard (COLIPA), which allows comparison between the products of various manufacturers.
Given the frequent uses of these substances over large areas, it is not ruled out that the high-dosed filters (approx. 3 to 30 wt. % of the formulation) are applied to the skin in gram quantities. However, these amounts of filter substances must have been dissolved and incorporated into the formulation in a homogeneous and stable manner.
Oily components, which have a good dissolving power for the filter substances, are often used to dissolve these substances. Certain ester oils, inter alia, are thus also employed. Aliphatic benzoic acid esters are a class of compounds which can be employed. A typical representative of this class of compounds is the compound Tegosoft® TN(C12-C15 Alkyl Benzoate), which is employed frequently as a solvent for UV light protection filters.
Numerous compounds are known for protection against UV-B radiation, usually derivatives of 3-benzylidenecamphor, of 4-aminobenzoic acid, of cinnamic acid, of salicylic acid, of benzophenone and also of 2-phenylbenzimidazole.
It is also important to have filter substances available for the range between about 320 nm and about 400 nm, the so-called UV-A range, since rays in this range can also cause damage. It has been proved that UV-A radiation leads to damage to the elastic and collagen fibres of connective tissue, which makes the skin age prematurely, and that it is to be regarded as the cause of numerous phototoxic and photoallergic reactions. The harmful influence of UV-B radiation may be intensified by UV-A radiation.
4,4′,4″-(1,3,5-Triazine-2,4,6-triyltriimino)-tris-benzoic acid tris(2-ethylhexyl ester), synonym: 2,4,6-tris-[anilino-(p-carbo-2′-ethyl-1′-hexyloxy)]-1,3,5-triazine, is a UV-B filter. This UV-B filter substance is marketed by BASF AG under the trade name UVINUL™ T 150 and is distinguished by good UV absorption properties.
The main disadvantage of this UV-B filter is the poor solubility in lipids. Known solvents for this UV-B filter can dissolve a maximum of approx. 15 wt. % of this filter, corresponding to about 1-1.5 wt. % of dissolved and therefore active UV light protection filter.
Isononyl benzoate is the ester of benzoic acid with isononanol. Isononyl benzoate is a compound which is known per se and employed as a fast-gelling, low-viscosity plasticizer for plastics (PVC, PAMA, PVB etc.) and adhesives and is marketed, inter alia, by Oxeno Olefinchemie GmbH under the trade name Vestinol® INB. Isononanol is listed, inter alia, under the Chemical Abstract Service (CAS) numbers 27458-94-2, 68515-81-1 or also 3452-97-9. Preparation is as a rule carried out by esterification of isononanol with benzoic acid, as described in DE 10217186. In this context, the esterification and treatment conditions can also be varied, as described, for example, in U.S. Pat. No. 6,635,775 for other benzoic acid esters.